Keep thimerosal in vaccines: pediatricians

NEW YORK (Reuters Health) - A mercury-containing preservative should not be banned as an ingredient in vaccines, U.S. pediatricians said Monday, in a move that may be controversial.

In its statement, the American Academy of Pediatrics (AAP) endorsed calls from a World Health Organization (WHO) committee that the preservative, thimerosal, not be considered a hazardous source of mercury that could be banned by the United Nations.

Back in 1999, a concern that kids receiving multiple shots containing thimerosal might get too much mercury - and develop autism or other neurodevelopmental problems as a result - led the AAP to call for its removal, despite the lack of hard evidence at the time.

"It was absolutely a matter of precaution because of the absence of more information," said Dr. Louis Cooper, from Columbia University in New York, who was on the organization's board of directors at the time.

"Subsequently an awful lot of effort has been put into trying to sort out whether thimerosal causes any harm to kids, and the bottom line is basically, it doesn't look as if it does," Cooper, who wrote a commentary published with the AAP's statement, told Reuters Health.

In a 2004 safety review, for example, the independent U.S. Institute of Medicine concluded there was no evidence thimerosal-containing vaccines could cause autism. A study from the Centers for Disease Control and Prevention came to the same conclusion in 2010.

With the exception of some types of flu shots, the compound is not used in vaccines in the United States, which are distributed in single-dose vials.

And nobody is arguing that should change, according to Dr. Walter Orenstein, a member of the AAP Committee on Infectious Diseases and a researcher at the Emory Vaccine Center in Atlanta.

But in countries with fewer resources - where many children still die of vaccine-preventable diseases - it's cheaper and easier to use multi-dose vials of vaccines against diphtheria and tetanus, for example.

Thimerosal prevents the rest of a multi-dose vial from getting contaminated with bacteria or fungi each time a dose is used.

Researchers estimated it could cost anywhere from two to five times as much to manufacture vaccines for developing countries without thimerosal, and both transporting vaccines and keeping them refrigerated would be much harder as well.

"If we had to take the thimerosal out of those multi-dose vials, we're having a hard time completing the task of getting every kid immunized now, that would add a tremendous burden," Cooper said - and more children would probably die as a result.

"Children who can now be protected from these life-threatening diseases could become vulnerable," Orenstein told Reuters Health.

The new statement is published in the AAP's journal Pediatrics.

Thimerosal contains a type of mercury called ethyl mercury. Toxic effects have been tied to its cousin, methyl mercury, which stays in the body for much longer.

Earlier this year, the WHO said replacing thimerosal with an alternative preservative could affect vaccine safety and might cause some vaccines to become unavailable.

Mercury, however, is still on the list of global health hazards to be banned in a draft treaty from the United Nations Environment Program - which would mean a ban on thimerosal.

Reducing mercury exposure "is a wonderful thing," Orenstein said.

However, "We need this exception because thimerosal is so vital for protecting children."

He said keeping thimerosal in vaccines is essential mostly for humanitarian reasons - although preventing childhood diseases in the developing world could also help the U.S. because other countries can serve as reservoirs for illness.

"For American parents, this is more looking at the world and our role and responsibility in protecting the children of the world than it is a direct impact," Orenstein said.